Sorry I've been bouncing around from active to inactive on this forum today! XD
In all truth if you're not going to use a filter I wouldn't buy a tank kit with one.
For light all you really need (especially for something as small as a 2.5 gallon) is a desk lamp. =]
The bulbs that you purchase for your lamp will definitely determine your success with planted tanks.
You'll want a Daylight (rated at 6,500 K(kelvins)) CFL (swirly energy-saving bulbs).
Here's an example of the packaging for one of more of these bulbs:
<-- The word Daylight and the Kelvin rating should be clearly visible somewhere on the package.
You only want about 2-3 watts per gallon. As this is difficult with 2.5 gallons I'd say just keep your lamp elevated above your tank. =] The smallets wattage I found was a 13 watt.
You'll also want to pick up an outlet timer from the hardware store so that you can time your light to be on for 4 hours, off for 4-5 hours and then back on for another 4-5 hours
Did I not include a plant list earlier? It might've been a different thread. XD
Marimo won't help you to "plant cycle" your tank no. It DOES look really cool though! ;]
Plants that help you to "Plant Cycle" your tank are fast growing stem plants.
Examples of some great fast-growing stem plants:
You'll likely only need one or two though. ;] As your tank is so small. and you'll likely only need a small amount.
To balance out all the different light greens I advise buying some Java Fern and an Anubias to add some dark green. The marimo would do that as well.
In my experience it's nearly impossibly to kill watersprite and anacharis. =] I've even almost frozen it and it's ok! =]
Really hardy plants (well... hornwort can be tricky but that's just hornwort).
Good luck with your tank! =]